The conformers of allyl alcohol and allyl mercaptan were studied with B3LYP/aug-cc-pVTZ method. Their relative energies were calculated at MP3, MP4（SDQ）, and CCSD（T） levels. The most stable conformers for these two molecules are Gauche-gauche＇ （Gg＇）. The theo-retical photoelectron spectra simulated with the calculated ionization energies demonstrate that there are at least four conformers in allyl alcohol and four conformers in allyl mercaptan in the gas-phase experiments. The Dyson orbitals of the highest occupied molecular orbital （HOMO） and the next HOMO （HOMO-1） of allyl mercaptan Ggt conformer show strongly mixing ns and πc=c characteristics, which may be due to the resonance and inductive effects between πc=c and ns in HOMO-1 and HOMO.
